In holographic recording for recording information onto a recording medium using holography, in general, the information light carrying image information and recording-specific reference light are overlapped with each other inside the recording medium and the interference fringe pattern generated thereby is written onto the recording medium. For reproducing the recorded information, reproduction-specific reference light is irradiated to the recording medium for diffracting the interference pattern so as to reproduce the image information.
Recently, in the field of the holographic recording for achieving super high density optical recording, volume holography, especially digital volume holography, has been developed to be in practical use and has attracted attention. The volume holography is a method in which the interference patterns are written three-dimensionally by actively utilizing the thickness direction of the recording medium as well. The digital volume holography is a computer-oriented holographic recording method in which image information to be recorded is limited to binary digital patterns, while using the same recording medium and the recording system as that of the volume holography. In the digital volume holography, for example, picture information such as an analog picture is once digitized to be two-dimensional digital pattern and then it is recorded as image information. At the time of reproduction, the digital pattern information is read out and decoded to be displayed as the original picture information. Thereby, even when SN ratio (signal-to-noise ratio) at the time of reproduction is not so good, it becomes possible to reproduce the information which notably faithfully reflects the original information by carrying out differential analysis or carrying out error correction by coding the binary data.
In an example of recording information to a hologram recording layer by the volume holography, information light carrying information to be recorded and recording-specific reference light are simultaneously irradiated from a transparent substrate side for a prescribed length of time so as to generate interference fringe in the thickness direction in the hologram recording layer, and the interference fringe pattern is three-dimensionally fixed within the hologram recording layer for recording the information as the three-dimensional hologram (Japanese Unexamined Patent Publication No. 11-311938 and Japanese Unexamined Patent Publication No. 2003-99952).
Further, as the optical information recording method, there are a method in which information light and recording-specific reference light are disposed on optical axes at different angles, and a method in which both are coaxially disposed.
The recording method in which information light and recording-specific reference light are coaxially disposed has drawn attention as a method more suitable for the above-described volume holography (for example, see Japanese Unexamined Patent Publication No. 10-124872).
Japanese Unexamined Patent Publication No. 11-311938
Japanese Unexamined Patent Publication No. 2003-99952
Japanese Unexamined Patent Publication No. 10-124872
U.S. Pat. No. 5,638,193